Inhibition and stimulation of leukocyte adherence by soluble factors from murine lymphocytes.

Activation of murine spleen cells with either specific antigen or mitogen resulted in the production of soluble factors capable of either inhibiting or stimulating the adherence of normal peritoneal cells. Leukocyte adherence inhibition factor (LAIF) and leukocyte adherence stimulation factor (LASF) were detected using the original leukocyte adherence inhibition (LAI) assay as performed with haemocytometers. An important factor in determining both the production and detection of adherence-modulating factors was the serum content in both the preparation and testing of supernatants favoured LAIF, whereas a lower serum content resulted in LASF predominating. With mitogen (concanavalin A) -activated cells, variable production of adherence inhibitory and stimulatory activities was found, but LASF appeared to be favoured at low concentrations of concanavalin A and serum. Adherence inhibitory and stimulatory factors in concanavalin A-generated spleen cell supernatants were separable on Sephacryl S-200 columns. LAIF had a molecular weight of less than 55,000 daltons, whereas most LASF activity was greater than 70,000 daltons. The occurrence of adherence-modulating factors with opposing effects may be a potential source of variability in LAI assays.